Progressive dielectric heating



March 20, 1951 T. P. KlNN 2,546,004

PROGRESSIVE DIELECTRIC HEATING Filed July 11, 1947 /8 /e ,14 54a. 52a 504. /O //O v INVENTOR 7Zea dare RIF/fin.

BY 9. zz fi m n ATTORNEY Patented Mar. 20, 1951 PROGRESSIVE DIELECTRIC HEATING Theodore P. Kinn, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 11, 1947, Serial No. 760,348

3 Claims.

My invention relates to dielectric heating systems having spaced heating-electrodes for heating material or work as it is conveyed between the heating-electrodes, the material or work being of a type which changes its dielectric characteristics or heating requirements as it is undergoing dielectric heating. Rayon, plastics, rubber and plywood are illustrations of materials to which my invention is applicable, but my invention is also useful with any similar material which, during dielectric heating, undergoes a change in a physical or chemical property which affects the voltage or voltage gradient to which the material should or may be subjected.

An object of my invention is to provide a dielectric heating system capable of introducing heating energy into material of a type described while the material is being conveyed on a conveyor, the energy being introduced at a uniform or controlled rate along different points of travel of the material.

Another object of my invention is to provide a dielectric heating system of a type described capable of heating traveling material at a maximum possible rate along all points of the system. In accordance with my invention, this objective is obtained by keepin the voltage-gradient in the material always at a high value, but insufiicient to cause puncture or other fiashover through or around the material.

It is a further object of my invention to provide a dielectric heating system of a type described comprising a plurality of pairs of heating-electrodes through which the material to be heated is successively passed; all pairs of heatingelectrodes being energized from a single highfrequency power line.

Still another object of my invention is to dielectrically heat moving material in a manner described and while the material is enveloped by a controlled or other atmosphere.

Another object of my invention is to provide a dielectric heating apparatus for heating moving material, the system comprising a housin inside of which sets or pairs of heating-electrodes are arranged successively along the path of travel in which the material moves through the housing, the sets of heating-electrodes being connected to a common source of high-frequency power through means which permit the voltage across each set of heating-electrodes to be individually adjusted or controlled from outside the housing. A specific object of my invention is to provide a dielectric heating system of a type described which can be safely adjusted from outside the housing in which the heating-electrodes are disposed.

Other features, objects and innovations of my invention, in addition to the foregoing, will be discernible from the following description of preferred and representative embodiments ,ofmy invention. The description is limited to such details as will enable an understanding of the invention and is to be taken in conjunction with the accompanyin drawing. In the drawing, in which like numerals represent corresponding parts:

Figure 1 is a simplified representation of an embodiment of my invention;

Fig. 2 is a simplified diagram of the electrical circuits found in an apparatus such as disclosed in Fig. 1; and

Figs. 3, 4 and 5 are simplified electrical diagrams of modified forms of electrical elements and connections that can be used in apparatus in accordance with Fig. 1 of my invention.

Referring to Fig. 1, a housing 2 is shown as comprising a main treating chamber ,4, an entrance 6 and an exit 8. An endless conveyor It has a work-ca rrying portion which passes through the treating chamber 4. The material, or work W, to be heated, is loaded onto the conveyor in front of the entrance 6 of the housing. The conveyor moves the material W through the housing for dielectric heating, after which the material is removed from the conveyor at a point beyond the exit end 8 of the housing. While traveling through the housin 2, the material passes between an arrangement of heating-electrodes comprising a lower metallic heating-electrode l2, and a plurality of upper insulated heat ing-electrodes l4, l6 and 18 arranged successively in the direction in which the material travels through the housing. The heating-electrodes l4, l6 and I8 are fiat metal plates and are coplanar, but are spaced so that each is electrically insulated from those adjacent to it. I

The Work W on the conveyor H] can be heated while enveloped by a controlled atmosphere inside the housing. To this end, the housing is provided with suitable inlets 20 and outlets 22- be simultaneously raised and lowered through any suitable and common mechanism shown as comprising a screw 24 of insulating material which is operated by a manually operable member in the form of a hand wheel 26 on the outside of the housing 2. Such adjustment can be used, if desired, to change the voltage across the pairs of heating-electrodes.

Power for heating the material passing between the heating-electrodes is obtained from a single power supply, such as a tank circuit, or from a transmission line of any suitable kind. For simplicity, a transmission line is shown. The line comprises a coaxial cable 28 having a grounded outer conductor 30 and an insulated inner conductor 32. The ground conductor 3i] is conductively connected to the lowerrheating-electrode [2. This can, of course, be accomplished by suitably grounding the heating-electrode l2. Conductors 34, 36 and 3B separately connect the inner conductor 32 to networks 49, 42 and M, respectively, each of which is individually associated with an insulated heating-electrode. This isfrepresentedin :Fig. 1 by :an insulated conductor 46 extending from each network to the -asso- 'ciated:heatingaelectrode- M 1-6 or i=8; as the case may be; after passing through: an insulating bushing 48 inthe top wall ofthe housing 2.

-"Energization of'the'powersupply line provides anelectric field between. the heating-electrodes I2 and 14, between the heating-electrodes -I 2 and I6,- and between the heating-electrodes. l2 and IBI Since the heating-electrodes i l; wand 18 are insulated from each other and'spa'c e'dedgc- WVlSB] the electric fields will be distinct. Hence, electrically considered, the heating-electrodes i2 snag HLform as'et or-"first pair of heating-electrodes;'the-=heating-electrodes l2 and lea-second pair, and the heating-electrodes H3 and 1-8 a third pair. In a sense, the same is true physicau since each of the'insulated' heating-electrodes l4, l6 and IS, in providing its associated electric field, ccoperateswith a portion of the heating-electrode l2 which is distinct frorrwthe portions of the heating-electrode l2 with which the'other' insulated heating-electrodes cooperate. Hence, the pair of heating-electrodes i2 and 14 form a capacitor 50, the pair of heatin'g electrodes l2 and I6 form a capacitor 52,- and the pair ofheating electrodes l2 and l8-form a eapacitor 54. The capacitance of-these capacitors will also depend on the material being heated. In order to keepthe heating time of the ma terial W to a minimum, it is desirable to provide a'voltage across the several pairs of heatingelectrodes l2- and I4, l2 and i6, i2 and I8, which will introduce a voltage-gradient through the work-that is as high as the workcan safely with-- stand-without damage to the work or-flas'hovers around the work. Such dielectric materials as rayonyresin or plywood, for example, cannot withstand a significant voltage-gradient or a large"- overall voltage during the initial part of the heating because of their relatively high moistu'recontent. However, as the material becomes drier or sets or cures, it usually can'ha've' a higher voltageegradientnacross it, and can withstand a higher" overall" voltage. The increased voltage or voltage-gradient results in more power being put into the "material-"so that the material can be more rapidly heated or it can be brought to a higher temperature in a shorter time.- It-is also sometimes desirable, for other reasons, to control the rate at which energy is introduced into the material in a portion of the complete heating cycle it undergoes while traveling through the housing. In accordance-with my invention, the networks 40, 42 and 44 are of a character which '.form known to the art.

reactances is preferably adjustable for the desired power transfer and voltage adjustment, as

closely as conditions. permit. A scheme for this purpose" is shownin Fig. 2 where the network is shown as comprising an L-C resonant circuit 7 in which. the capacitance is made up of a pair of heating-electrodes and its heating load therebetween. In Fig. 2, the equivalent of the heating-electrode [2 of Fig. 1 has been shown as consisting of three-separate smaller heating-electrodes [2a, 'l'Zb-and- I20. Thesection 12a 00- operates with the heating-electrode i4; and the sections I21) and l 20 cooperate with the heatingelectrodes 56 and lfl'respectively. The material to be heated is carried successively'between the pairs of heating-electrodes lZrlI. and I4, I21) and It, or and M3, by the conveyor It. The-several pairs of heating-electrodes and the dielectric material therebetween form capacitors 50a, 52a and 54a, respectively. Connectedacross each capacitor-555a, 52a and 54a, is a variable inductive coil 56, 58-a-nd .60, respectively, which is preferably, but not necessarily, of -:a ereacta-nce, at the. supply frequency-whichapproximates or is-somewhat higher than that of its associated capacitor, but can be adjusted to-much lower values. Theinsulated-conductor 32 of the power transmission line is separately adjustably' connected to each inductive coil through a variable inductor 62 and a manipulatable tap t4 adjust ably contactingdiiferent points of the associated inductive coil. In Fig. l, an insulated ma-nipu lator for moving a tap is shown as a hand wheel 66 on an adjusting shaft 63 which protrudes from a suitable box that contains the associated network elements.

A further and important advantage of the adjustable networks'resides in the fact that they can be changed so as to compensate for the change in'the capacity of the several pairs of heating-electrodes which occurs when the heating-electrodes'are adjusted through operation of the hand wheel 26. Accordingly,'the addition of the .adjustable networks also makes the apparatus more universal for treating materials of different heights, dielectric constants and loss factors.

, In; Fig. 2, the voltage acrossjthepairs of heatingeelectrodes will. usually be at or .above the line voltage. Byiinserting "variabIeLcapacitQrs min the connections to the netwo'rksgas shown in.-Fig. 3, the voltageia'crossthe 'pairstof heatingelectrodescan be lowered to values below. that of the line; and-.impedance-ma-tching restored by changing'the tap-point on the inductive coils 56, 58 and 60.

.Figs. 4 and 5 illustrate further forms of the many networks which can be interposed between the powersupply .line and the pairs of heatingelectrodes for enabling the voltage across the pairs of heating-electrodes to be more readily adjusted in accordance with the voltage required forheating the work at the desired rate. In Fig. 4, a T' network '72 is provided-for each pair of embodiment lies in the fact that the moving plates through which the capacitors 14 are adjusted, can be grounded. In Fig. 5, a variable capacitor 16 is connected in parallel with each pair of heating-electrodes, and a variable inductor 18 is in the connection of each parallel circuit-arrangement to the conductor 32.

In general, if a network has the net effect of an inductive reactance, the voltage across the associated pair of heating-electrodes will be raised as compared to the voltage on the line, and if the net effect of the network is that of a capacitance then the voltage on the pair of heatingelectrodes will be lowered. By suitable connections, as shown, for example in Figs. 4 and 5, a movable member of the networks can be grounded.

While I have described my invention in various forms, it is obvious that many equivalents can be substituted, and that principles of my invention can be applied in many different embodiments.

I claim as my invention:

1. Dielectric heating equipment comprising a housing, a conveyor having a material-carrying portion inside said housing and a loading portion outside said housing, a plurality of pairs of heating-electrodes inside said housing, each pair comprising heating-electrodes on opposite sides of said material-carrying portion of said conveyor, one of each of said pair of heating-electrodes being insulated from the associated heating-electrode paired therewith and from a heating-electrode of a different pair, common means for adjusting said insulated heating-electrodes to vary the spacing thereof with respect to the associated heating-electrodes, a high-frequency power line outside said housing, a plurality of networks at said housing, there being a separate network for each pair of heating-electrodes, and conductor means connecting said networks to said power line and connecting each of said networks separately to an individual pair of said heating-electrodes, each of said networks comprising an adjustable reactance member, and means outside said housing for adjusting said reactance member, each network and the associated pair of heating-electrodes forming a tunable load cir cuit.

2. Equipment for the dielectric heating of dielectric material, conveyor means adapted to move dielectric material, said equipment comprising a plurality of pairs of heating-electrodes, each pair comprising relatively insulated heating-electrodes spaced from each other, the spaces between the heating-electrodes of the respective pairs merging and being arranged to form a substantially straight path through which a particular portion of the material can be substantially rectilinearly moved by said conveyor means from a position between a first pair of said heat-- ing-electrodes to a position between a next succeeding pair of said heating-electrodes, each of the last said pairs including relatively insulated heating-electrodes which lie on the same side of said path but are spaced from each other in the general direction in which the material moves, means supporting an insulated heating-electrode of each of said pairs relatively movable with respect to the associated heating-electrode for varying the spacing therebetween a single source of high-frequency energy comprising an insulated power-conductor, and circuit-branch means connecting said single source of energy to said pairs of heating-electrodes, said circuit-branch means including a network comprising a separately adjustable inductance connected between said power-conductor and said adjustably supported heating-electrode of a first of said pairs of heating-electrodes, and a variable capacitance across the last said pair of heating-electrodes.

3. An invention including that of claim 2 but characterized by said variable capacitance having a grounded adjusting element.

THEODORE P. KINN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,309,303 Crandell Jan. 26, 1943 2,321,131 Crandell June 8, 1943 2,403,800 Hoyler July 9, 1946 2,415,025 Grell et a1. Jan. 28, 1947 2,421,334 Kline et al May 27, 1947 2,428,615 Brown Oct. 7, 1947 2,432,412 Hacklander Dec. 9, 1947 2,436,732 Rowe Feb. 24, 1948 2,458,012 Madsen Jan. 4, 1949 2,464,403 Klingaman Mar. 15, 1949 2,464,404 Gillespie Mar. 15, 1949 

